Introduced more than half a century ago, fiber-reinforced plastics are composite materials with a wide range of applications in industry, for example in the aerospace, automotive, chipping, building and construction industries. A reinforced article can comprise any combination of individual materials, for example a thermoplastic polymer (the matrix) in which fibers (reinforcing fiber) have been dispersed. A great diversity of organic fibers, including synthetic fibers such as polyamide, polytetrafluoroethylene, polyesters, natural fibers such as cotton, hemp, flax, jute and inorganic fibers, such as glass fibers and carbon fibers are often used as reinforcing fibers in composite materials.
The reinforced plastics industry has been using glass fibers in different forms for reinforcing polymer matrices to produce a diversity of products. Glass fibers are generally supplied as a plurality of continuous, very long filaments, and can be in the form of strands, rovings or yarns. A filament is an individual fiber of reinforcing material. A strand is a plurality of bundled filaments. Yarns are collections of filaments or strands twisted together. A roving refers to a collection of strands wound into a package.
A process for producing reinforced compositions is for example described in WO2009/080281. In this publication a process is described for producing a long glass fiber-reinforced thermoplastic polymer composition, which comprises the subsequent steps of:                a. Unwinding from a package of at least one continuous glass multifilament strand containing a sizing composition;        b. Applying an impregnating agent to said at least one continuous glass multifilament strand to form an impregnated continuous multifilament strand;        c. Applying a sheath of thermoplastic polymer around the impregnated continuous multifilament strand to form a sheathed continuous multifilament strand; and        d. Cutting the sheathed continuous glass multifilament strand into pellets.        
The pellets that are obtained with the above-described process comprise a multifilament glass strand that has the same length as the pellet. When these pellets are molded into an article the stiffness of the article is not sufficient in all cases. The stiffness of an article can be raised by raising the amount of glass fibers in the article. However, pellets which contain a higher amount than 50 wt % of glass fibers cannot be used in injection molding processes. Moreover with increasing glass fibre content the weight of the final part will increase which is not always desirable in particular not in the automotive industry.
The manufacture of fiber reinforced thermoplastic moulded product is known for example from U.S. Pat. No. 6,291,064. This patent discloses a fibre reinforced thermoplastic resin pellet comprising a thermoplastic resin as a matrix polymer and glass fibres as the reinforcing fibres, wherein the length of the pellet is about 2 to 12 mm, the glass fibres having substantially the same length as the pellet are contained in an amount of 20 to 60 vol % of the total pellet, in the state of aligned or twisted fibres along the longitudinal direction of the pellet, and L/D2 is 0.45 or more and L/D is from 1.1 to 6 wherein L represents the length of the pellet and D represents the diameter thereof. The pellet disclosed in this US patent is blended with a resin pellet which does not substantially contain any glass fibre, and then the blend can be injection moulded to produce the moulded product.